Circa is an iPhone app that logs your supplements, caffeine, and nicotine in two taps and pairs them with your Google Fitbit Air data to turn the two into trend insights, audited correlations, and a live forecast for tonight's sleep. Everything is computed on your iPhone. There is no Circa account and no Circa server. Circa is free and shows advertising, which is loaded over the network.
PRECISE INPUTS
Log anything in two taps: exact dose, exact unit, exact time. Your stack is a shortcut, never a constraint — type any amount, switch units freely (mg, g, µg, IU, pouch, ml, drops). One-tap logging from the Lock Screen widget, or just tell Siri "Log an espresso in Circa."
STIMULANT PHARMACOKINETICS
Live caffeine and nicotine decay curves against your bedtime, with the 50 mg caffeine threshold drawn where it matters. See what this afternoon's espresso still costs you at 23:00.
AUDITED INSIGHTS
Every effect ships with its receipts: n, 95% confidence interval, p-value, correlation — and the actual nights behind it as a scatter plot. Insights that fail their interval for 14 days are retired automatically. Honest null results included.
TONIGHT, FORECAST
A transparent driver model predicts tonight's sleep score and deep-sleep minutes from what you actually did today. Every driver shows its signed contribution. It recomputes on every log — watch the number move.
A 104-SUPPLEMENT LIBRARY
Goal-ranked, evidence-graded, interaction-flagged. Pick your goals and the library re-ranks itself around you.
YOUR DATA STAYS YOURS
Health data is read from the Google Health API and processed entirely on-device. Disconnecting revokes access and erases everything. Export anytime as CSV and JSON.
Explore the full app in demo mode before connecting anything.
Circa is a personal tracking tool, not a medical device. It does not diagnose, treat, or prevent any condition. Requires a Google Fitbit Air and a Google account for live data; manual logging and demo mode work without one.
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